Ireland coach Joe Schmidt says his side will be judged on how they respond to a shock World Cup defeat against hosts Japan in Shizuoka on Saturday.

Japan produced a stunning 19-12 victory to leave Ireland boss Schmidt feeling "incredibly disappointed".

Schmidt, who bemoaned the penalty count from referee Angus Gardner after his side lost a 12-3 lead, said he was not surprised by Japan's performance.

"It's not the first time we've seen them do it," he said.

"It's not a surprise to us that they were incredibly tough to beat.

"It unfortunately met my expectations. We expected them to be as good as they were. We knew they were going to be incredibly tough and so it proved."

Ireland beat Scotland in their opening match at the World Cup but Japan's surprise victory leaves Pool A wide open.

"The strength of the team will be how they respond and rebound from this," said Schmidt, whose side still have to face Russia and Samoa.

"A six-day turnaround was a little bit tough and we've got a five-day turnaround now into the Russian game in Kobe on Thursday. So that will be another challenge for us."

Schmidt felt "three or four" penalties given against Ireland for offsides were "pretty tough" and gave Japan the momentum.

Australian referee Gardner took charge of Saturday's match, and tries from Garry Ringrose and Rob Kearney appeared to have the Irish in control. But amazingly Ireland, the world's top-ranked side at the start of the tournament, were held scoreless for the remainder of the contest.

"We're incredibly disappointed that we didn't manage to control the end of the game but they are a tremendous side," added the Ireland coach.

"Congratulations to Japan. What a furious, intense effort it was. We knew it was potentially coming."

Schmidt has 'no regrets' over Sexton omission

The Ireland coach said that he had no regrets about leaving out fly-half star Johnny Sexton as Jack Carty started before being replaced by Joey Carbery in the second half.

Sexton was not risked because of a thigh strain and while Carty helped set up Ireland's two first-half tries, he began to struggle in the second half with Carbery's introduction not helping to stem the tide.

"I don't think you ever regret utilising your squad because we were here four years ago and we kind of didn't use the squad. We didn't want to make that mistake again," added Schmidt.

"I thought he [Carty] controlled the first half pretty well but once we came under pressure on the back of some penalties they got that field position."

Ireland captain Rory Best denied that the Irish had been caught unawares by the Japan onslaught.

"We knew how tough it was going to be. Anyone who is utterly shocked hasn't seen how good they were," Best told BBC Radio 5 Live.

"We had a game plan and were prepared. We made a few mistakes and were on the wrong side of the penalty count.

"But Japan played really well and posed us a lot of questions. Unfortunately we couldn't come up with the right answers."

Best admitted that the lively Japanese display left the Irish "chasing shadows".

"When you play the host team it's always tough. We didn't start how we wanted and we let them play.

"You have to give credit to Japan - they attacked us minute after minute. We have to dust ourselves down and get better."